This invention relates to fabrication of solid state structures, and more particularly relates to dimensional control of solid state structural features.
Precise dimensional control of solid state structural features is essential for many applications in fields ranging from biology and chemistry to physics, optics, and microelectronics. The term xe2x80x9csolid statexe2x80x9d is here meant to refer to non-biological materials generally. Frequently the successful fabrication of a solid state system critically depends on an ability to articulate specific structural features, often of miniature dimensions, within very tight tolerances. Accordingly, as solid state systems evolve to the microregime and further to the nano-regime, nanometric dimensional feature control is increasingly a primary concern for system feasibility.
There have been established a wide range of microfabrication techniques for producing and controlling structural feature dimensions in micromechanical and microelectromechanical systems. For example, high resolution lithographic techniques and high-precision additive and subtractive material processing techniques have been proposed to enable small-scale feature fabrication. But in the fabrication of many nano-regime systems, in which structural feature dimensions of a few nanometers are of importance, it is generally found that conventionally-proposed techniques often cannot form the requisite nano-scale features reproducibly or predictably, and often cannot be controlled on a time scale commensurate with production of such nano-scale features. As a result, volume manufacture of many systems that include nanometric feature dimensions and/or tolerances is not practical or economical.
The invention provides processes that enable reproducible and predictable production of structural features for solid state mechanical or electromechanical systems. The processes of the invention can be controlled to produce feature dimensions in the nano-regime and can include real time feedback control operating on a time scale commensurate with the formation of nano-scale solid state features.
In one technique provided by the invention, for controlled fabrication of a solid state structural feature, a solid state structure is provided and exposed to a fabrication process environment the conditions of which are selected to produce a prespecified feature in the structure. A physical detection species is directed toward a designated structure location during process environment exposure of the structure, and the detection species is detected in a trajectory from traversal of the designated structure location. This provides an indication of changing physical dimensions of the prespecified feature. The fabrication process environment is controlled in response to physical species detection to fabricate prespecified physical dimensions of the structural feature.
xe2x80x9cSolid-statexe2x80x9d is used herein to refer to materials that are not of biological origin. By biological origin is meant naturally occurring, i.e., isolated from a biological environment such as an organism or cell, or otherwise occurring in nature, or a synthetically manufactured version of a biologically available structure, or a synthetic or non-naturally occurring homologue or derivative of a naturally occurring material that substantially retains the desired biological traits of interest. Solid-state encompasses both organic and inorganic materials.
The structure can be provided as, e.g., a substrate of inorganic or material, or crystalline material, and can be provided as a semiconductor wafer, a membrane, a layer in which the prespecified feature is to be fabricated, or other suitable structure.
The fabrication process can be provided as, e.g., a sputtering environment such as ion beam or electron beam sputtering; as a wet chemical etch environment, such as an electrochemical etch environment; as a plasma environment; as a chemomechanical polishing environment; as an ion-induced or ion-assisted environment; as an environment for material deposition or growth; as a heating environment, or as another suitable environment.
In one example, the prespecified feature is an aperture, and the fabrication process conditions are selected to etch the aperture. Here the detection species trajectory can be through the aperture. An array of apertures can be formed in such a manner. The fabrication process conditions can be selected to enlarge or to reduce the aperture diameter.
Similarly, the prespecified feature can be a trench, a slot, or a gap between at least two structural edges, with the fabrication process conditions selected to enlarge or to reduce the trench, slot, or gap. The detection species trajectory can be through the trench, slot, or gap.
The detection species can be provided as atoms, ion, electrons, an etch species provided in the fabrication process environment, or other species. The species detection can be carried out by detecting the existence of the detection species in a trajectory from traversal of the designated structure location. The species detection further can be carried out by quantifying the detection species as a function of time. The fabrication process environment can be controlled by terminating exposure of the structure to the process environment at a point in time when the species detection indicates fabrication of prespecified dimensions of the structural feature.
This process can be applied, in accordance with the invention, to fabricate an aperture in a solid state structure. In this process, there is to be provided a solid state structure having a first surface and an opposing second surface. On the first structure surface is formed a cavity extending to a cavity bottom located at a point between the first and second structure surfaces. Then the structure is thinned from the second structure surface. A physical detection species is directed toward a location on the structure for the aperture as defined by the cavity, during the structure thinning, and the physical detection species is detected in a trajectory through the aperture when thinning of the structure causes the second structure surface to intersect with the cavity bottom. The structure thinning is controlled based on physical detection species detection.
This technique can be employed to produce an aperture of a prespecified diameter by quantifying the detected physical detection species during the structure thinning and then controlling the structure thinning based on the quantification to produce a prespecified aperture diameter.
The structure can be provided as a membrane, e.g., a silicon nitride membrane. The thinning can be carried out by any suitable process, e.g., sputtering. The detection species can be, e.g., ions or electrons, and the detection species can be distinct from a species employed for thinning the structure.
The invention also provides techniques for controlling a physical dimension of a solid state structural feature. In an example of such a process, a solid state structure having a structural feature is provided, and the structure is exposed to a flux of ions at a selected structure temperature. The exposure conditions are selected to cause at least one physical dimension of the feature to be changed substantially by transport of material of the structure to the structural feature in response to the ion flux exposure. Similarly, to fabricate a physical feature on the solid state structure, the structure is exposed to a flux of ions at a selected structure temperature. The exposure conditions are selected to produce a physical feature on the structure substantially by transport of material of the structure to the structural feature in response to the ion flux exposure.
The exposure condition control can include, e.g., control of structure temperature, control of ion flux, energy, species, or time structure, control of ambient gas species, or control of another suitable parameter of the exposure.
These processes can enable an increase or a decrease in feature dimensions, e.g., reduction in diameter of an aperture, reduction in a trench width, reduction in a gap width, or increase in a protrusion height. The structure can be provided as a crystalline substrate, a membrane, e.g., a silicon nitride membrane, or other structure. The ion flux can be provided as flux from a focused ion beam. In one example, a first membrane surface is exposed to ion flux to produce a protrusion on a second membrane surface opposite the first membrane surface. The physical species detection mechanisms described above can be employed to control ion flux exposure to change or produce a feature in a prespecified manner.
These processes enable fabrication of a wide range of structural features in a manner that is reproducible, controllable, and efficient. Applications in fields ranging from biology to microelectronics are enabled by these processes, and can be carried out in a manner that is commercially viable. Other features and advantages of the invention will be apparent from the following description and associated drawings, and from the claims.